World no. 2 Roger Federer disappointed more than 17,000 fans at the O2 Arena after pulling out of the final against Novak Djokovic, citing a back injury sustained in his semifinal match against Stanislas Wawrinka.
The 33-year-old Swiss announced he was "not match-fit" as he apologised to the crowd in person.
The withdrawal resulted in Djokovic's fourth victory at the season-ending event. He also becomes the first man to win three titles in a row since Ivan Lendl back in the 80s.
No one saw that coming from Federer, who had withdrawn during tournaments on only two previous occasions - in 2008 against James Blake (Bercy) and 2012 against Jo-Wilfried Tsonga (Doha).
|Novak Djokovic won seven ATP events in 2014, including Wimbledon.|
Federer declined to speak to the media on Sunday night after his withdrawal.
On Monday Federer and Wawrinka are due to travel to Lille where, starting on Friday, they will joining the Switzerland team that tackles France in the Davis Cup. That is the only major prize in tennis that the Swiss maestro has not won.